1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method and, more particularly, to an ink jet printing apparatus and an ink jet printing method in which the amount of ink ejected from a printing head onto a printing medium can be varied for each of ejection ports of the printing head.
2. Description of the Related Art
Printing apparatus included in printers, copiers, and facsimile machines and things like that and printing apparatus used as output apparatus for composite electronic equipment including a computer or word processor or workstations or the like are configured to print images (including characters and the like) on a printing surface of a printing medium such as a sheet of paper or a plastic thin plate based on image information (including character information and the like). Printing apparatus are generally categorized into ink jet type, wire-dot type, thermal type, and laser beam type apparatus according to the printing method. Among those printing apparatus, ink jet type printing apparatus (hereinafter referred to as “ink jet printing apparatus”) perform printing by ejecting ink from an ink ejecting unit of a printing head onto a printing medium. In comparison to other types of printing, ink jet printing apparatus are characterized in that high definition can be easily achieved; high speed and quietness is excellently achieved; and they are provided at a low cost. The spread of color scanners and digital cameras has resulted in increasing needs for color printing. Many ink jet printing apparatus capable of color printing have been developed to satisfy such needs.
In order to achieve an improved printing speed, an ink jet printing apparatus has a printing head provided with a plurality of printing elements integrated and arranged. The printing head used is a unit obtained by integrating a plurality of ink ejection ports and liquid channels as ink ejecting units. In general, an ink jet printing apparatus has a plurality of printing heads to support for color printing.
FIG. 1 shows a configuration of a printing unit of an ink jet printing apparatus for performing printing on a printing surface of a printing medium P. In the same figure, reference numeral 101 represents an ink cartridge. The ink cartridge 101 has ink tanks which are filled with inks in four colors, e.g., black, cyan, magenta, and yellow, respectively, and a printing head 102 having an ejection port array for each ink color. An ejection port array of the printing head 102 is an arrangement of a plurality of ejection ports. The printing head 102 performs printing by ejecting ink droplets from each of the ejection ports.
FIG. 2 is a view of one of the ejection port arrays taken in the direction z in FIG. 1. Reference numeral 201 represents a plurality of ejection ports arranged to constitute the ejection port array. In one ejection form among a plurality of forms of ejection that are available, for example, in a configuration in which a heating-heater is provided in the vicinity of each ejection port, heat is generated at the this heating-heater to generate bubbles in ink when the ink is ejected, and the ink is ejected by a pressure generated by the bubbles. Other forms of ejection include a piezoelectric form or the like.
Referring again to FIG. 1, reference numeral 103 represents a sheet conveying roller which rotates in the direction of the arrow in the figure while holding the printing medium P in cooperation with an auxiliary roller represented by 104. As a result, the printing medium P is conveyed in the direction y in accordance with a printing operation of the printing head 102. Reference numeral 105 represents a pair of sheet feeding rollers which feeds the printing medium P and also plays a role of holding the printing medium P similarly to the sheet conveying roller 103 and the auxiliary roller 104. Reference numeral 106 represents a carriage which supports the four ink cartridges 101 and which moves the cartridges in the direction of the arrow x during printing. The carriage 106 is moved in the direction of the arrow x by driving means and drive controlling means which are omitted in the illustration. The carriage 106 stands by in a home position (h) indicated by the dotted line in the figure when printing is not performed or when an operation of recovering the printing head 102. Specifically, when a printing start instruction from the drive control means arrives the carriage 106 which is in the home position h before printing is started, the carriage 106 is moved in the direction of the arrow x, and the printing head 102 of the ink cartridge 101 ejects ink droplets from the plurality of ejection ports 201 based on data supplied thereto to perform printing. When the data is recorded by the printing head 102 up to an end of the printing surface of the printing medium P, the carriage 106 is returned to the home position h, and the sheet conveying roller 103 conveys the printing medium P by a predetermined amount. Printing; and sheet conveying are alternately repeated in such a manner to perform printing on the entire printing surface of the printing medium P.
Many proposals have been made on printing apparatus in a configuration in which a plurality different-sized dots are formed on a printing surface of a printing medium in order to perform printing with a multiplicity of gradations.
The invention disclosed in Japanese Patent Application Laid-Open No. 8-183179(1996) discloses a configuration which ink droplets to be ejected from one ejection port are changed into a plurality different-sized dots to eject(e.g. in FIG. 4, a configuration in which a plurality of heaters are located in an ejection port is disclosed). The above official gazette discloses that plural different-sized ink droplets can be ejected from ejection ports corresponding to sizes of ink droplets ejected (e.g. see FIGS. 21 to 26).